Most streams flow into another body of water. Some streams flow into another stream, while others flow into a lake or the ocean. Any time a stream flows into another body of water, it is a tributary of that other body of water. Very often, small brooks join together and become tributaries of creeks, and then those creeks are tributaries of rivers. Those rivers, in turn, are tributaries of bigger rivers. Find and look at a map of the United States. You can see that the Mississippi River has many tributaries, and all those tributaries have tributaries too! Does water from a creek near your home eventually flow from one stream to another and finally into this mighty river? If so, you live in the Mississippi River watershed.